Vascular disease, which is the principal cause of heart attack, stroke and circulatory deficit disorders, is responsible for 50 percent of all mortality in the western world. Proliferation of vascular smooth muscle cells (VSMCs) is a key step in the pathogenesis of atherosclerosis and restenosis after vascular interventions such as angioplasty. Much attention has been focused on the search for an antiproliferative agent to regulate smooth muscle proliferation. Interferons (IFNs), which are cytokines secreted by the immune cells present in the atherosclerotic lesion, have been show to be antiproliferative towards VSMCs. Natural glycosaminoglycans such as heparin are also known to inhibit smooth muscles. Heparin is used widely as one of the local-delivery drugs after invasive procedures. In spite of the well-documented antiproliferative effects of IFNs and heparin on VSMCs, the molecular mechanisms that are involved have not yet been identified. PKR (protein kinase, RNA activated) is an IFN induced, growth inhibitory protein kinase, which is activated by double stranded (ds) RNA in virus-infected cells. PKR's role in regulation of cell proliferation has become clear in recent years. It's over expression or activation has been shown to be growth inhibitory. PKR is also activated by heparin in vitro and our results indicate that treatment of VSMCs with heparin results in activation of PKR. PKR is also induced at the transcriptional level by IFN treatment of VSMCs We hypothesize that, PKR is involved in mediation both heparin and IFN's antiproliferative effect towards VSMCs. We propose to test this with the following specific aims: 1. To investigate the role of PKR in the antiproliferative action of heparin and IFN on VSMCs. 2. To characterize the functional domains of PKR involved in mediating heparin's antiproliferative effect. The long-term goal of this proposal is to elucidate the molecular mechanisms involved in the inhibition of VSMC grown by heparin and IFN thereby offering on opportunity to design better ways of controlling the vascular diseases.